SQL Server Reporting Services (SSRS) is a web based reporting system produced by Microsoft. Originally made available as a free download, from SQL Server 2005 onwards it is bundled with SQL Server and is not available separately.
Reporting Services comes with several major components:
The report server, which publishes reports through a web interface, manages security on reports and various other functions.
Report Designer, included in B.I. Development Studio (bundled with SQL Server) this allows a developer to make reports backed by bespoke queries. It can consume data from relational, OLAP and various other sources. Reports built with Report Designer can be published to a report server.
Report Builder, an ad-hoc reporting tool that can act as a front-end to database or OLAP data sources. Report builder provides a drag/drop style interface for building reports, which can be published to a report server and viewed through the server's web interface.